Separate Track Impact Factor Application Depending on Track Types through Correlative Analysis with Track Support Stiffness
Round 1
Reviewer 1 Report
At the beginning I would like to congratulate the authors of the extensive research. I am surprised that the stiffness of the ballasted track is greater than the stiffness of the ballastless slab track. Based on formulas 1-a, 1-b and 2, I conclude that it should be inverserly. The stiffness of the reinforced concrete slab is greater than ballast and sleepers, especially for Rheda type slab, in which the embedded sleeper is also used. In addition, subgrade stiffness is required higher for ballasless than ballasted track. Is it related to the use of flexible anti-vibration mats or pads?
305-308 error, it should be: In ballast‐less slab track, the TSS calculated by trackside measurement is about 37~98% larger than the theoretical TSS and 7~23% larger in ballasted track.
In conclusions the same error, lines 351-353
Author Response
On behalf of all the authors who participated in the writing of this humble article, I would like to express my utmost gratitude for taking the time out of your busy schedule to review our paper.
We prepared the responses to your comments and you can find the details below, and we are hopeful that the revisions we have made to the article are in accord with the comments you provided for us.
Comment 1:
At the beginning I would like to congratulate the authors of the extensive research. I am surprised that the stiffness of the ballasted track is greater than the stiffness of the ballastless slab track. Based on formulas 1-a, 1-b and 2, I conclude that it should be inversely. The stiffness of the reinforced concrete slab is greater than ballast and sleepers, especially for Rheda type slab, in which the embedded sleeper is also used. In addition, subgrade stiffness is required higher for ballastless than ballasted track. Is it related to the use of flexible anti-vibration mats or pads?
Response 1:
Firstly, thank you kindly once again for your words of encouragement.
However, with regards to the stiffness values of the ballasted and ballastless slab tracks, we would like to attempt the following response;
As you indicated the stiffness of the individual components may be higher (when comparing the ballast and sleepers of the ballasted tracks to that of the concrete slab in the ballastless slab tracks), but the stiffness of the track that are discuss in the formulas (1-a, 1-b, 2) is that of track modulus, not track stiffness (we have revised the paper to make this point clearer). When the track support stiffness is calculated in the trackside measurement, we are discussing “track stiffness,” it is more common that the ballasted tracks have higher TSS than ballastless slab tracks. Please refer to page 79 of Konstantinos Tzanakakis’ The Effect of Track Stiffness on Track Performance https://link.springer.com/chapter/10.1007%2F978-3-642-36051-0_16 for details.
In general, when the overall modulus of elasticity of the track is low (which indicates low differential settlement rate of the overall ballastless track structure), the load applied from the train on to the track foundation is reduced while the rail displacement is relatively large (which makes the structure require flexible anti-vibration mats or pads for noise reduction).
In the case of ballasted track, the differential settlement throughout the track structure is high due to high modulus of elasticity, and the rail displacement due to wheel load is relatively smaller than that of ballastless tracks while the effect of the wheel load applied on the overall track structure down to the foundation of the ballast layer and subsoil (high settlement rate of the overall ballasted track structure) in consideration of the different layers becomes large. With this principle in mind, normal circumstances show the overall track support stiffness of ballast-less slab track (calculated by the ratio of dynamic wheel load over rail displacement) being higher than ballasted tracks. A thesis by Henrik Lund confirms this (Transition zones between ballasted and ballastless tracks (2014) http://lup.lub.lu.se/luur/download?func=downloadFile&recordOId=4498421&fileOId=8961741, page 22)
“The track stiffness varies depending on the track construction, substructure and soil quality. As mentioned earlier, an abrupt change in vertical track stiffness will give rise to a disruption of the vehicle gait due to the change in track deflection. Despite of perfect track alignments the change in vertical track stiffness will result in a response from the vehicle. The response causes supplementary dynamic forces, which in turn may influence the track degradation, comfort experience, and cause increased vibrations, to name a few. The accelerated track degradation in the transition zone will in time result in deteriorated track alignment, which in turn causes increased dynamic forces and further acceleration of the degradation process (ibid.).
The modulus of subgrade reaction is a measure of the subgrade stiffness at the lower edge of the sleeper, specified as the ratio between the contact pressure against a medium, e.g. soil, and indentation the pressure causes. The modulus is mostly used as a measure when calculating settlements under a fundament on soil. It is almost being considered a spring constant depending on the size of the load and propagation (Nationalencyklopedien 1, 2014).
It is noticeable that the stiffness below the sleeper can, in extreme cases vary in the order of a factor ten. The variations in stiffness are equalised by the characteristic load distribution of the track through the flexural stiffness in the rails, and the flexibility provided by the URP, USP etc. (Nyström & Prokopov, 2011).
The flexural stiffness of the superstructure is thus of great importance regarding to the variation of track stiffness. A higher resilience in the superstructure leads to smaller variations in track stiffness (ibid.).
Therefore, the track support stiffness measurement values that are being compared in the results, as well as those that used for standard track structure stability assessment, is that of the stiffness of the superstructure (mainly by the displacement of the rail), which is why in the measurement results, it is common to see the track support stiffness of ballastless tracks being lower than that of ballasted tracks.
The article will be revised to clarify this point in Section 1 (introduction) and Section 2.1. Please refer of the revised version of the paper for details.
Comment 2:
305-308 error, it should be: In ballast‐less slab track, the TSS calculated by trackside measurement is about 37~98% larger than the theoretical TSS and 7~23% larger in ballasted track.
Response 2: The article has been revised accordingly. Thank you kindly for pointing out this error.
Comment 3:
In conclusions the same error, lines 351-353
Response 3: The article has been revised accordingly. Thank you kindly for pointing out this error.
We hope that the above response to your inquiries and comments suffice. We extend our gratitude to you once again for your attention and care in the drafting of our article.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The paper deals with determining the impact factor for ballasted and ballastless tracks. The starting point is that in some countries' design standards the impact factor does not depend on the track type. Based on the measurement results, different correlations between impact factor and track stiffness for ballasted and ballastless tracks have been developed. It was concluded that it could be recommended to national authorities of some countries (such as Korea) to change the standard where the impact factor would be calculated differently for ballasted and ballastless tracks.
The scientific contribution of this research is poorly justified. It is a well-known fact that the impact factor depends on the dynamic effect of wheel and rail irregularities, and that the dynamic effect of wheel depends on truck stiffness, which is differently determined for ballasted and ballastless tracks.
The literature review is very poor and does not include recent research in this area published in major journals. Out of a total of 15 references, only 4 were published in international journals. Others have been published at conferences or in the Journal of the Korean Society for Railway.
Author Response
On behalf of all the authors who participated in the writing of this humble article, I would like to express my utmost gratitude for taking the time out of your busy schedule to review our paper.
We prepared the responses to your comments and you can find the details below, and we are hopeful that the revisions we have made to the article are in accord with the comments you provided for us.
Comment 1:
The scientific contribution of this research is poorly justified. It is a well-known fact that the impact factor depends on the dynamic effect of wheel and rail irregularities, and that the dynamic effect of wheel depends on truck stiffness, which is differently determined for ballasted and ballastless tracks.
Response 1:
As you so kindly pointed out, the scientific merit of this research may not be as high when compared to other types of research papers on the field of railway engineering.
However, it seems that the point of our paper was not clearly presented due to a lack of more recent literature review. The fact of the matter is track support stiffness (or track stiffness at wheel rail contact point) is a factor that is only considered in few standards in the international setting, and as far as the authors are concerned, only the British Railways considers this parameter for calculating dynamic factors. While it is true that the facts of impact factor depending on the dynamic effect of wheel and rail irregularities, and the dynamic effect of wheel depending on track stiffness should be a common knowledge, the practice of calculating dynamic factor (track impact factor) using TSS is not common, at least in as evidenced in our paper, Korea, China, Middle East, and South East Asia. Brandon J. Van Dyk et. Al (https://journals.sagepub.com/doi/abs/10.1177/0954409715619454) offers a fairly recent paper on the existing different types of impact factor calculation and the parameters considered.
Furthermore, for most trackside measurement, track support stiffness at wheel-rail contact point is measured by the ratio of wheel load and displacement of the rail, in which case the measurement of TSS, while the method remains the same for ballasted and ballast-less tracks.
In general, when the overall modulus of elasticity of the track is low (which indicates low differential settlement rate of the overall ballastless track structure), the load applied from the train on to the track foundation is reduced while the rail displacement is relatively large (which makes the structure require flexible anti-vibration mats or pads for noise reduction).
In the case of ballasted track, the differential settlement throughout the track structure is high due to high modulus of elasticity, and the rail displacement due to wheel load is relatively smaller than that of ballastless tracks while the effect of the wheel load applied on the overall track structure down to the foundation of the ballast layer and subsoil (high settlement rate of the overall ballasted track structure) in consideration of the different layers becomes large. With this principle in mind, normal circumstances show the overall track support stiffness of ballast-less slab track (calculated by the ratio of dynamic wheel load over rail displacement) being higher than ballasted tracks. A thesis by Henrik Lund confirms this (Transition zones between ballasted and ballastless tracks (2014) http://lup.lub.lu.se/luur/download?func=downloadFile&recordOId=4498421&fileOId=8961741, page 22)
“The track stiffness varies depending on the track construction, substructure and soil quality. As mentioned earlier, an abrupt change in vertical track stiffness will give rise to a disruption of the vehicle gait due to the change in track deflection. Despite of perfect track alignments the change in vertical track stiffness will result in a response from the vehicle. The response causes supplementary dynamic forces, which in turn may influence the track degradation, comfort experience, and cause increased vibrations, to name a few. The accelerated track degradation in the transition zone will in time result in deteriorated track alignment, which in turn causes increased dynamic forces and further acceleration of the degradation process (ibid.).
The modulus of subgrade reaction is a measure of the subgrade stiffness at the lower edge of the sleeper, specified as the ratio between the contact pressure against a medium, e.g. soil, and indentation the pressure causes. The modulus is mostly used as a measure when calculating settlements under a fundament on soil. It is almost being considered a spring constant depending on the size of the load and propagation (Nationalencyklopedien 1, 2014).
It is noticeable that the stiffness below the sleeper can, in extreme cases vary in the order of a factor ten. The variations in stiffness are equalised by the characteristic load distribution of the track through the flexural stiffness in the rails, and the flexibility provided by the URP, USP etc. (Nyström & Prokopov, 2011).
The flexural stiffness of the superstructure is thus of great importance regarding to the variation of track stiffness. A higher resilience in the superstructure leads to smaller variations in track stiffness (ibid.).
Therefore, the track support stiffness measurement values that are being compared in the results, as well as those that used for standard track structure stability assessment, is that of the stiffness of the superstructure (mainly by the displacement of the rail), which is why in the measurement results, it is common to see the track support stiffness of ballastless tracks being lower than that of ballasted tracks.
In order to make the point of our paper more clear on this matter, we revised the paper’s introduction and conclusion. Please refer to the revised Section 1, Section 2.1 and Section 4 for details.
Comment 2:
The literature review is very poor and does not include recent research in this area published in major journals. Out of a total of 15 references, only 4 were published in international journals. Others have been published at conferences or in the Journal of the Korean Society for Railway.
Response 2:
In light of this situation with variety of the existing impact factor calculation methods, and as pointed out by various authors, there is an evident lack of clarity and standardization on which parameters to consider, and this is particularly problematic in places such as Korea, Middle East, and South East Asia where the fast historical development of railway system by importing technologies from overseas led to stable railway operation, but poor design and maintenance standards. There is also a significant problem in over-designing of ballast-less track structures as well as most maintenance work and track stability evaluation conducted in Korea does not take into account key parameters (such as track support stiffness) for calculating the track impact factor and criteria for track quality index (including rail irregularities) calculation criteria is shared for both ballasted and ballastless tracks (derailment coefficient, wheel load fluctuation, wheel load, stress and rail displacement). A even bigger problem is that while this is a prevalent issue, problems that are associated with track maintenance mishaps between ballasted and ballastless tracks are rarely documented and made available to the general public. which is why related sources in the international journals are not yet found, and we had to rely heavily in Korean sources. The actual types of reference that are really relevant to this topic are either in Korea (where the issue has just recently been discussed in conferences but made difficult to clarify due to lack of cooperation from railway companies) or are simply non-existent in international major journals, as other nations most likely do not face similar problems as Korea and countries with similar situations do. Still, we have included more references published in international journals to enhance the quality of the paper. This paper attempts to clarify these related risks and clearly distinguish that at the very least, impact factors for ballasted and ballastless tracks should be calculated differently due to the difference in the track stiffness.
We hope that the above response to your inquiries and comments suffice. We would like to extend our gratitude to you once again for your attention and care in the drafting on this article.
Author Response File: Author Response.docx
Reviewer 3 Report
This manuscript focuses on the method evaluating track impact factor that considers the effect of track type in addition to other conventional parameters dynamic wheel load and speed. The proposed method can differentiate between ballasted and ballast‐less slab track structures. The manuscript discusses the limitation of track impact factor determination method as prescribed by KR‐C 14030 and other methods in the literature. The use of linear regression is often not correct due to significant over prediction of track impact factor at high train speeds. The literature review is not balanced and several important studies pertaining to this topic of the research are not cited. Some examples include:
Jenkins, H. H., Stephenson, J. E., Clayton, G. A., Morland, G. W., and Lyon, D. (1974). “The effect of track and vehicle parameters on wheel/rail vertical dynamic forces.” Railway Eng. J., 3(1), 2–16.
Nimbalkar, S. and Indraratna, B. (2016). “Improved performance of ballasted rail track using geosynthetics and rubber shockmat”, J. Geotech. Geoenviron. Eng., 10.1061/(ASCE)GT.1943-5606.0001491
Priest, J. A., and Powrie, W. (2009). “Determination of dynamic track modulus from measurement of track velocity during train passage." J. Geotech. Geoenviron. Eng., 10.1061/(ASCE)GT.1943-5606.0000130.
The primary objectives of the study are not clearly outlined. The present manuscript does not contain much novelty although the presentation and interpretation of track impact factors is interesting. The conclusion needs to be succinct while focusing clearly on the primary findings of the study.
In view of the above, major revision is necessary.
Author Response
On behalf of all the authors who participated in the writing of this humble article, I would like to express my utmost gratitude for taking the time out of your busy schedule to review our paper.
We prepared the responses to your comments and you can find the details below, and we are hopeful that the revisions we have made to the article are in accord with the comments you provided for us.
Comment 1:
The use of linear regression is often not correct due to significant over prediction of track impact factor at high train speeds.
Response 1:
As you have pointed out, linear regression was revised, and the risk of representing this data as a linear regression was highlighted in the discussion in Section 4.2 (please refer to the revised document for details.) However, a trend line was still placed for reference purposes for a clearer visual comparison.
Comment 2:
The literature review is not balanced and several important studies pertaining to this topic of the research are not cited. Some examples include:
Jenkins, H. H., Stephenson, J. E., Clayton, G. A., Morland, G. W., and Lyon, D. (1974). “The effect of track and vehicle parameters on wheel/rail vertical dynamic forces.” Railway Eng. J., 3(1), 2–16.
Nimbalkar, S. and Indraratna, B. (2016). “Improved performance of ballasted rail track using geosynthetics and rubber shockmat”, J. Geotech. Geoenviron. Eng., 10.1061/(ASCE)GT.1943-5606.0001491
Priest, J. A., and Powrie, W. (2009). “Determination of dynamic track modulus from measurement of track velocity during train passage." J. Geotech. Geoenviron. Eng., 10.1061/(ASCE)GT.1943-5606.0000130
Response 2:
In light of this situation with variety of the existing impact factor calculation methods, and as pointed out by various authors, there is an evident lack of clarity and standardization on which parameters to consider, and this is particularly problematic in places such as Korea, Middle East, and South East Asia where the fast historical development of railway system by importing technologies from overseas led to stable railway operation, but poor design and maintenance standards.
There is also a significant problem in over-designing of ballast-less track structures as well as most maintenance work and track stability evaluation conducted in Korea does not take into account key parameters (such as track support stiffness) for calculating the track impact factor and criteria for track quality index (including rail irregularities) calculation criteria is shared for both ballasted and ballastless tracks (derailment coefficient, wheel load fluctuation, wheel load, stress and rail displacement).
A even bigger problem is that while this is a prevalent issue, problems that are associated with track maintenance mishaps between ballasted and ballastless tracks are rarely documented and made available to the general public.
Which is why related sources in the international journals are not yet found, and we had to rely heavily in Korean sources. The actual types of reference that are really relevant to this topic are either in Korea (where the issue has just recently been discussed in conferences but made difficult to clarify due to lack of cooperation from railway companies) or are simply non-existent in international major journals, as other nations most likely do not face similar problems as Korea and countries with similar situations do. Still, we have included more references published in international journals to enhance the quality of the paper (There are now 26 references in total in the revised document)
This paper attempts to clarify these related risks and clearly distinguish that at the very least, impact factors for ballasted and ballastless tracks should be calculated differently due to the difference in the track stiffness.
Comment 3
The primary objectives of the study are not clearly outlined. The present manuscript does not contain much novelty although the presentation and interpretation of track impact factors is interesting. The conclusion needs to be succinct while focusing clearly on the primary findings of the study.
Response 3:
As you so kindly pointed out, the present manuscript may not contain much novelty when compared to other types of research papers on the field of railway engineering.
However, it seems that the point of our paper was not clearly presented due to a lack of more recent literature review.
The fact of the matter is track support stiffness (or track stiffness at wheel rail contact point) is a factor that is only considered in few standards in the international setting, and as far as the authors are concerned, only the British Railways considers this parameter for calculating dynamic factors. While it is true that the facts of impact factor depending on the dynamic effect of wheel and rail irregularities, and the dynamic effect of wheel depending on track stiffness should be a common knowledge, the practice of calculating dynamic factor (track impact factor) using TSS is not common, at least in as evidenced in our paper, Korea, China, Middle East, and South East Asia. Brandon J. Van Dyk et. Al (https://journals.sagepub.com/doi/abs/10.1177/0954409715619454) offers a fairly recent paper on the existing different types of impact factor calculation and the parameters considered.
Furthermore, for most trackside measurement, track support stiffness at wheel-rail contact point is measured by the ratio of wheel load and displacement of the rail, in which case the measurement of TSS, while the method remains the same for ballasted and ballast-less tracks.
In general, when the overall modulus of elasticity of the track is low (which indicates low differential settlement rate of the overall ballastless track structure), the load applied from the train on to the track foundation is reduced while the rail displacement is relatively large (which makes the structure require flexible anti-vibration mats or pads for noise reduction).
In the case of ballasted track, the differential settlement throughout the track structure is high due to high modulus of elasticity, and the rail displacement due to wheel load is relatively smaller than that of ballastless tracks while the effect of the wheel load applied on the overall track structure down to the foundation of the ballast layer and subsoil (high settlement rate of the overall ballasted track structure) in consideration of the different layers becomes large. With this principle in mind, normal circumstances show the overall track support stiffness of ballast-less slab track (calculated by the ratio of dynamic wheel load over rail displacement) being higher than ballasted tracks. A thesis by Henrik Lund confirms this (Transition zones between ballasted and ballastless tracks (2014) http://lup.lub.lu.se/luur/download?func=downloadFile&recordOId=4498421&fileOId=8961741, page 22)
“The track stiffness varies depending on the track construction, substructure and soil quality. As mentioned earlier, an abrupt change in vertical track stiffness will give rise to a disruption of the vehicle gait due to the change in track deflection. Despite of perfect track alignments the change in vertical track stiffness will result in a response from the vehicle. The response causes supplementary dynamic forces, which in turn may influence the track degradation, comfort experience, and cause increased vibrations, to name a few. The accelerated track degradation in the transition zone will in time result in deteriorated track alignment, which in turn causes increased dynamic forces and further acceleration of the degradation process (ibid.).
The modulus of subgrade reaction is a measure of the subgrade stiffness at the lower edge of the sleeper, specified as the ratio between the contact pressure against a medium, e.g. soil, and indentation the pressure causes. The modulus is mostly used as a measure when calculating settlements under a fundament on soil. It is almost being considered a spring constant depending on the size of the load and propagation (Nationalencyklopedien 1, 2014).
It is noticeable that the stiffness below the sleeper can, in extreme cases vary in the order of a factor ten. The variations in stiffness are equalised by the characteristic load distribution of the track through the flexural stiffness in the rails, and the flexibility provided by the URP, USP etc. (Nyström & Prokopov, 2011).
The flexural stiffness of the superstructure is thus of great importance regarding to the variation of track stiffness. A higher resilience in the superstructure leads to smaller variations in track stiffness (ibid.).
Therefore, the track support stiffness measurement values that are being compared in the results, as well as those that used for standard track structure stability assessment, is that of the stiffness of the superstructure (mainly by the displacement of the rail), which is why in the measurement results, it is common to see the track support stiffness of ballastless tracks being lower than that of ballasted tracks.
In order to make the point of our paper more clear on this matter, we revised the paper’s introduction and conclusion. Please refer to the revised Section 1, Section 2.1 and Section 4 for details.
We hope that the above have responded appropriately to your inquiries and comments. We would like to extend our gratitude to you once again for all your attention and care in the drafting of this manuscript.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
The manuscript has been significantly improved.
Reviewer 3 Report
The manuscript is recommended for the publication.
